Node.js返回MySQL查询结果 [英] Node.js returning result from MySQL query

问题描述

我有以下函数从数据库获取一个十六进制代码

I have the following function that gets a hexcode from the database

function getColour(username, roomCount)
{
    connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
    {
        if (err) throw err;
        return result[0].hexcode;
    });
}

$ b $ p我的问题是我在回调函数中返回结果，但getColour函数不返回任何内容。我想让getColour函数返回 result [0] .hexcode 的值。

在我调用getColour的时候它不返回任何东西

At the moment when I called getColour it doesn't return anything

function getColour(username, roomCount)
{
    var colour = '';
    connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
    {
        if (err) throw err;
        colour = result[0].hexcode;
    });
    return colour;
}

但当然SELECT查询已经完成时返回 color

but of course the SELECT query has finished by the time return the value in colour

推荐答案

你必须对db的结果进行处理仅查询回调。就像

You have to do the processing on the results from the db query on a callback only. Just like.

function getColour(username, roomCount, callback)
{
    connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
    {
        if (err) 
            callback(err,null);
        else
            callback(null,result[0].hexcode);

    });

}

//call Fn for db query with callback
getColour("yourname",4, function(err,data){
        if (err) {
            // error handling code goes here
            console.log("ERROR : ",err);            
        } else {            
            // code to execute on data retrieval
            console.log("result from db is : ",data);   
        }    

});

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